Problem: Kevin has dinner at a restaurant and the cost of his meal is $\$39.00$. He would like to leave a $20\%$ tip. What is his total bill including tip?
The tip amount is equal to $20\% \times \$39.00$ We can find the tip by first calculating a $10\%$ tip and then multiplying that number by two. To calculate a $10\%$ tip, move the decimal point in $\$39.00$ one place to the left. $10\%$ $\times \$39.00$ $\$3.90$ To calculate a $20\%$ tip, multiply the $10\%$ tip amount by two. $20\%$ $\times \$39.00$ $\$3.90$ $ \times 2 = $ $\$7.80$ The cost of the meal plus the amount of the tip will equal the total bill amount. $\$39.00 + \$7.80 = $ $\$46.80$ The total cost of the bill is $\$46.80$.